The invention relates to a dewatering member with a composite body for a paper or board machine and to a method for manufacturing a dewatering member with a composite body for a paper or board machine.
In paper machines, among other things, different suction boxes, loading elements, etc. are used for dewatering, in which boxes and elements a foil structure is often used in which the foils, on the one hand, support or load a wire/felt and, on the other hand, doctor the water being drained from the paper web off the surface of the wire. The foils are subjected to heavy wear against the wire, and therefore the foils shall be made of a material that is especially resistant to wear.
A problem in these prior art arrangements which have used a foil made of a ceramic has also been caused by the fact that ceramic materials do not ordinarily withstand high stresses. The present applications of dewatering devices require relatively narrow foils, which are very difficult to manufacture out of ceramic. Narrow ceramic foils are also very problematic from the standpoint of the stresses caused by loading.
Foils made of ceramic have also been problematic in that ceramic pieces may have risen from the desired level, with the result that the surface level of the foil structure that guides the wire and determines its run is not even any more.
With respect to the prior art, reference is made to FI application publication 940884, which discloses a method for manufacturing a structure comprising a set of foils for a dewatering device of a paper machine, and a structure comprising a set of foils for a dewatering device of a paper machine. In this prior art arrangement, a foil in the structure of a set of foils is attached to a frame structure of a web forming and/or dewatering device or to an equivalent support piece, and the surface of the foil facing the wire has been machined to a desired level or shape, after which the surface of the foil facing the wire has been coated with a ceramic coating, which is in direct contact with the foil body.
With respect to the prior art, reference is also made to FI application publication 943777, which discloses a dewatering member for a paper machine and a method for manufacturing it. In this prior art arrangement, the dewatering member comprises a body and a ceramic wearing surface. The body comprises an elongated profile which forms a bounded space into which it has been possible to cast a flowing material. The body has also included at least one surface for attaching the wearing surface. The body comprises thermoset plastic which fills the bounded space at least partly. The wearing surface is a ceramic coating thermally sprayed onto the surface of the body profile.
Today, the dewatering foils used in paper and board machines are manufactured of piece ceramic attached to a body. Small ceramic pieces made by sintering are attached to the body either mechanically or by gluing. A problem with piece ceramic has been, among other things, the “piano-key effect” in which glued ceramic pieces rise to different levels on the surface of the foil. In that case, the pieces which have risen to a higher level produce harmful marks on the paper web that is being manufactured. One problem with the prior art dewatering members has also been that pieces have become detached or split.